This invention relates to a fine or precision rotation mechanism for slightly rotating an object to a desired position with high precision.
Recently, an electron beam drawing system, a reduced scale projection type transfer system and an X-ray lithography system have been developed as a system for forming a fine pattern on an object such as a semiconductor wafer and a mask substrate. This type of apparatus requires a driving mechanism for slightly moving a sample with great precision on the order of submicrons. High precision fine driving mechanisms are required not only for the systems mentioned above, but also in fields where precise measurement is required.
Fine driving mechanisms include those in which an object is moved linearly in one direction and those in which an object is rotated. The prior art fine rotation mechanisms for causing rotational motion have the following problems. With a driving mechanism where the rotational stroke is large, it is difficult to obtain a slight motion. On the other hand, with a driving mechanism where slight motion is possible, it is impossible to provide a large rotational stroke.
For example, a literature entitled "Operating Characteristics of Motor-Driven Positioning Mechanisms" Autumn Meeting of the Precision Machine Association, 1976, p. 359, discloses a rotation mechanism in which a material having a piezoelectric effect is stressed to produce a rotational motion. With this rotation mechanism, an object can be moved only very slightly in an area with a radius of 29 mm for a very small rotational stroke of .+-.2 .mu.m. A rotation mechanism which is used of the piezoelectric effect is disclosed in U.S. Pat. No. 3,952,215 issued Apr. 20, 1976, "Stepwise Fine Adjustment", Sakitani. The disclosed machine is of a type in which an object is moved linearly and stepwise. To convert this motion to a rotational motion, it is necessary to use a conventional rotational table having a bearing. Further, to avoid rattling, it is necessary to use a rotation mechanism using a cantilever system or the like making use of the elastic deformation of a material. In this apparatus, the rotational stroke cannot be much increased. If it is increased too much, the bearing provided in the rotational table is liable to rattle. The rotational mechanism having a cantilever again cannot solve the problem of the insufficient rotational stroke.